Pro-Israel groups have set sights on unseating this progressive lawmaker. Will they succeed?

In total, outside groups have spent more than $12m to support Bell as opposed to $3m for Bush.

After Bush moved up the street, Hoelting told the Guardian her questions were prompted by UDP advertising landing at her door.

Bush acknowledged that the UDP ads were having an impact.

Bush said that most voters accept her reasoning but it leaves some undecided. In contrast, she said her position on Gaza almost never gets brought up on the doorstep.

This leaves Bush all the more frustrated by the influence on the campaign of pro-Israel lobby money, much of which comes from billionaires who also donate to Republicans.

Other major funding has come from a long list of Republican donors including the billionaire hedge fund founders Jonathon Jacobson, Paul Singer and Bernard Marcus, the founder of Home Depot, all of whom are outspoken supporters of Israel.

Still, the timing of his switch has fuelled suspicions.